SIMPLE J. Rosenberg
Internet-Draft jdrosen.net
Intended status: Informational February 16, 2013
Expires: August 20, 2013
SIMPLE made Simple: An Overview of the IETF Specifications for InstantMessaging and Presence using the Session Initiation Protocol (SIP)draft-ietf-simple-simple-09
Abstract
The IETF has produced many specifications related to Presence and
Instant Messaging with the Session Initiation Protocol (SIP).
Collectively, these specifications are known as SIMPLE - SIP for
Instant Messaging and Presence Leveraging Extensions. This document
serves as a guide to the SIMPLE suite of specifications. It
categorizes the specifications and explains what each is for and how
they relate to each other.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 20, 2013.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Internet-Draft Simple Made Simple February 20131. Introduction
The IETF has produced many specifications related to Presence and
Instant Messaging with the Session Initiation Protocol (SIP)
[RFC3261]. Collectively, these specifications are known as SIMPLE -
SIP for Instant Messaging and Presence Leveraging Extensions. These
specifications cover topics ranging from protocols for subscription
and publication, to presence document formats, to protocols for
managing privacy preferences. The large number of specifications can
make it hard to figure out exactly what exactly SIMPLE is, what
specifications cover it, what functionality it provides, and how
these specifications relate to each other.
This document serves to address this problem. It provides an
enumeration of the protocols which make up the SIMPLE suite of
specifications from IETF. It categorizes them into related areas of
functionality, and briefly explains the purpose of each and how the
specifications relate to each other. Each specification also
includes a letter that designates its category in the standards track
[RFC2026]. These values are:
S: Standards Track (Proposed Standard, Draft Standard, or Standard)
E: Experimental
B: Best Current Practice
I: Informational
2. Presence
SIMPLE provides for both presence and IM capabilities. Though both
of these fit underneath the broad SIMPLE umbrella, they are well
separated from each other and are supported by different sets of
specifications. That is a key part of the SIMPLE story; presence is
much broader than just IM, and it enables communications using voice
and video along with IM.
The SIMPLE presence specifications can be broken up into:
o The core protocol machinery, which provides the actual SIP
extensions for subscriptions, notifications and publications
o Presence documents, which are XML documents that provide for rich
presence and are carried by the core protocol machinery
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Internet-Draft Simple Made Simple February 2013
o Privacy and policy, which are documents for expressing privacy
preferences about how those presence documents are to be shown (or
not shown) to other users
o Provisioning, which describes how users manage their privacy
policies, buddy lists and other pieces of information required for
SIMPLE presence to work
o Optimizations, which are improvements in the core protocol
machinery that were defined to improve the performance of SIMPLE,
particularly on wireless links
2.1. Core Protocol MachineryRFC 6665, SIP-Specific Event Notification (S): RFC 6665 [RFC6665]
defines the SUBSCRIBE and NOTIFY methods for SIP, forming the core
of the SIP event notification framework. To actually use the
framework, extensions need to be defined for specific event
packages. Presence is defined as an event package [RFC3856]
within this framework. Packages exist for other, non-presence
related functions, such as message waiting indicators and dialog
state changes.
RFC 3856, A Presence Event Package for SIP (S): RFC 3856 [RFC3856]
defines an event package for indicating user presence through SIP.
Through this package, a SIP user agent can ask to be notified of
the presence state of a presentity (presence entity). The content
of the NOTIFY messages in this package are presence documents,
discussed in Section 2.2, below.
RFC 4662, A Session Initiation Protocol (SIP) Event Notification
Extension for Resource Lists (S): RFC 4662 [RFC4662] defines an
extension to RFC 6665 that allows a client to subscribe to a list
of resources using a single subscription. The server, called a
Resource List Server (RLS) will "expand" the subscription and
subscribe to each individual member of the list. Its primary
usage with presence is to allow subscriptions to "buddy lists".
Without RFC 4662, a UA would need to subscribe to each presentity
individually. With RFC 4662, they can have a single subscription
to all buddies. A user can manage the entries in their buddy list
using the provisioning mechanisms in Section 2.4, below.
RFC 5367, Subscriptions to Request-Contained Resource Lists in the
Session Initiation Protocol (SIP) (S): [RFC5367] is very similar to
RFC 4662. It allows a client to subscribe to a list of resources
using a single subscription. However, with this mechanism, the
list is included within the body of the SUBSCRIBE request. In RFC4662, it is provisioned ahead of time on the server.
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Internet-Draft Simple Made Simple February 2013RFC 3903, SIP Extension for Event State Publication (S): RFC 3903
[RFC3903] defines the PUBLISH method. With this method, a user
agent can publish its current state for any event package,
including the presence event package. Once an agent publishes its
presence state, the presence server would send notifications of
this state change using RFC 3856.
2.2. Presence Documents
Once a user has generated a subscription to presence using the core
protocol machinery, they will receive notifications (SIP NOTIFY
requests) which contain presence information. That presence
information is in the form of an XML presence document. Several
specifications have been defined to describe this document format,
focusing on rich, multimedia presence.
RFC 3863, Presence Information Data Format (S): [RFC3863] defines
the baseline XML format for a presence document. It defines the
concept of a tuple as representing a basic communication modality,
and defines a simple status for it (open or closed).
RFC 4479, A Data Model for Presence (S): [RFC4479] extends the basic
model in RFC 3863. It introduces the concepts of devices and
person status, and explains how these relate to each other. It
describes how presence documents are used to represent states in
communications systems in a consistent fashion. More than RFC3863, it defines what a presence document is and what it means.
RFC 4480, RPID: Rich Presence Extensions to PIDF (S): [RFC4480] adds
many more attributes to the presence document schema, building
upon the model in RFC 4479. It allows for indications of
activities, moods, places and place types, icons, and indications
of whether a user is idle or not.
RFC 4481, Timed Presence Extensions to the Presence Information Data
Format (PIDF) to Indicate Status Information for Past and Future Time
Intervals (S): [RFC4481] adds additional attributes to the presence
document schema, again building upon the model in RFC 4479. It
allows documents to indicate status for the future or the past.
For example, a user can indicate that they will be unavailable for
voice communications from 2pm to 3pm, due to a meeting.
RFC 4482, CIPID: Contact Information for the Presence Information
Data Format (S): [RFC4482] adds attributes to the presence document
schema for contact information, such as a vCard, display name,
homepage, icon, or sound (such as the pronunciation of their
name).
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Internet-Draft Simple Made Simple February 2013RFC 5196, Session Initiation Protocol (SIP) User Agent Capability
Extension to Presence Information Data Format (PIDF) (S): [RFC5196]
adds even more attributes to the presence document schema, this
time to allow indication of capabilities for the user agent. For
example, the extensions can indicate whether a UA supports audio
and video, what SIP methods it supports, and so on.
2.3. Privacy and Policy
The rich presence capabilities defined by the specifications in
Section 2.2 introduces a strong need for privacy preferences. Users
must be able to approve or deny subscriptions to their presence, and
indicate what information such watchers can see. In SIMPLE, this is
accomplished through policy documents, uploaded to the presence
server using the provisioning mechanisms in Section 2.4.
RFC 4745, Common Policy: A Document Format for Expressing Privacy
Preferences (S): [RFC4745] defines a general XML framework for
expressing privacy preferences for both geolocation information
and presence information. It introduces the concepts of
conditions, actions and transformations that are applied to
privacy-sensitive data. The common policy framework provides
privacy-safety, a property by which network error or version
incompatibilities can never cause more information to be revealed
to a watcher than the user would otherwise desire.
RFC 5025, Presence Authorization Rules (S): [RFC5025] uses the
framework of RFC 4745 to define a policy document format for
describing presence privacy policies. Besides basic yes/no
approvals, this format allows a user to control what kind of
information a watcher is allowed to see.
RFC 3857, A Watcher Information Event Template Package for SIP (S):
[RFC3857], also known as watcherinfo, provides a mechanism for a
user agent to find out what subscriptions are in place for a
particular event package. Though it was defined to be used for
any event package, it has particular applicability for presence.
It is used to provide reactive authorization. With reactive
authorization, a user gets alerted if someone tries to subscribe
to their presence, so that they may provide an authorization
decision. Watcherinfo is used to provide the alert that someone
has subscribed to a user's presence.
RFC 3858, An Extensible Markup Language (XML) Based Format for
Watcher Information (S): [RFC3858] is the companion to RFC 3857. It
specifies the XML format of watcherinfo that is carried in
notifications for the event template package in RFC 3857.
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Internet-Draft Simple Made Simple February 20132.4. Provisioning
Proper operation of a SIMPLE presence system requires that several
pieces of data are correctly managed by the users and provisioned
into the system. These include buddy lists (used by the resource
list subscription mechanism in RFC 4662) and privacy policies (such
as those described by the XML format in [RFC5025]).
In SIMPLE, management of this data is handled by the XML
Configuration Access Protocol (XCAP) [RFC4825]. XCAP is used by the
user agent to manipulate buddy lists, privacy policy, and other data
that is represented by XML documents stored on a server.
RFC 4825, The Extensible Markup Language (XML) Configuration Access
Protocol (XCAP) (S): [RFC4825] specifies XCAP. XCAP is a usage of
HTTP that allows a user agent to manipulate the contents of XML
documents stored on a server. It can be used to manipulate any
kind of XML, and the protocol itself is independent of the
particular schema of the data it is modifying. XML schemas have
been defined for buddy lists, privacy policies and offline
presence status, allowing all of those to be managed by a user
with XCAP.
RFC 5875, An Extensible Markup Language (XML) Configuration Access
Protocol (XCAP) Diff Event Package (S): [RFC5875] defines an
extension to the SIP user agent configuration profile, allowing a
user agent to learn about changes in its documents on an XCAP
server. With this mechanism, there can be a change made by
someone else to a buddy list or privacy policy document, and a UA
will find out that a new version is available.
RFC 5874, An Extensible Markup Language (XML) Document Format for
Indicating A Change in XML Configuration Access Protocol (XCAP)
Resources (S): [RFC5874] defines an XML format for indicating
changes in XCAP documents. It makes use of an XML diff format
defined in [RFC5261]. It is used in conjunction with [RFC5875] to
alert a user agent of changes made by someone else to their
provisioned data.
RFC 4826, XML Formats for Representing Resource Lists (S): [RFC4826]
defines two XML document formats used to represent buddy lists.
One is simply a list of users (or more generally, resources), and
the other defines a buddy list whose membership is composed of a
list of users or resources. These lists can be manipulated by
XCAP, allowing a user to add or remove members from their buddy
lists. The buddy list is also accessed by the resource list
server specified in RFC 4662 for processing resource list
subscriptions.
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Internet-Draft Simple Made Simple February 2013RFC 4827, An Extensible Markup Language (XML) Configuration Access
Protocol (XCAP) Usage for Manipulating Presence Document Contents
(S): [RFC4827] defines an XCAP usage that allows a user to store an
"offline" presence document. This is a presence status that is
used by a presence server when there are no presence documents
published for that user by any user agents currently running.
2.5. Federation
Federation refers to the interconnection of different presence and
instant messaging systems for the purposes of communications.
Federation can be between domains or within a domain. A document has
been developed which describes how presence and IM federation works.
RFC 5344, Presence and Instant Messaging Peering Use Cases (I):
[RFC5344] describes a basic set of presence and instant messaging
use cases for federating between providers.
2.6. Optimizations
When running over wireless links, presence can be a very expensive
service. Notifications often get sent when the change is not really
relevant to the watcher. Furthermore, when a notification is sent,
it contains the full presence state of the watcher, rather than just
an indication of what changed. Optimizations have been defined to
address both of these cases.
RFC 4660, Functional Description of Event Notification Filtering
(S): [RFC4660] defines a mechanism that allows a watcher to include
filters in its subscription. These filters limit the cases in
which notifications are sent. It is used in conjunction with RFC4661 [RFC4661] which specifies the XML format of the filters
themselves. The mechanism, though targeted for presence, can be
applied to any SIP event package.
RFC 4661, An Extensible Markup Language (XML)-Based Format for Event
Notification Filtering (S): [RFC4661] defines an XML format used
with the event notification filtering mechanism defined in RFC4660 [RFC4660].
RFC 5262, Presence Information Data format (PIDF) Extension for
Partial Presence (S): [RFC5262] defines a new XML format for
representing changes in presence documents, called a partial PIDF
document. This format contains an XML patch operation [RFC5261],
that, when applied to the previous presence document, yields the
new presence document. The partial PIDF document is included in
presence notifications when a watcher indicates that they support
the format.
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Internet-Draft Simple Made Simple February 2013RFC 5263, SIP Extension for Partial Notification of Presence
Information (S): [RFC5263] defines a mechanism for receiving
notifications that contain partial presence documents.
RFC 5264, Publication of Partial Presence Information (S):
[RFC5264] defines a mechanism for publishing presence status using
a partial PIDF document.
RFC 5261, An Extensible Markup Language (XML) Patch Operations
Framework Utilizing XML Path Language (XPath) Selectors (S):
[RFC5261] defines an XML structure for representing changes in XML
documents. It is a form of "diff", but specifically for XML
documents. It is used by several of the optimization mechanisms
defined for SIMPLE.
RFC 5112, The Presence-Specific Static Dictionary for Signaling
Compression (Sigcomp) (S): [RFC5112] defines a dictionary for usage
with Signaling Compression (Sigcomp) [RFC3320] to improve the
compressability of presence documents.
RFC 6446, Session Initiation Protocol (SIP) Event Notification
Extension for Notification Rate Control (S): [RFC6446] This document
specifies mechanisms for adjusting the rate of SIP event
notifications. These mechanisms can be applied in subscriptions
to all SIP event packages.
3. Instant Messaging
SIMPLE defines two modes of instant messaging. These are page mode
and session mode. In page mode, instant messages are sent by sending
a SIP request that contains the contents of the instant message. In
session mode, IM is viewed as another media type - along with audio
and video - and an INVITE request is used to set up a session that
includes IM as a media type. While page mode is more efficient for
one or two message conversations, session mode is more efficient for
longer conversations since the messages are not sent through the SIP
servers. Furthermore, by viewing IM as a media type, all of the
features available in SIP signaling - third party call control,
forking, and so on, are available for IM.
3.1. Page ModeRFC 3428, Session Initiation Protocol (SIP) Extension for Instant
Messaging (S): [RFC3428] introduces the MESSAGE method, which can be
used to send an instant message through SIP signaling.
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Internet-Draft Simple Made Simple February 2013RFC 5365, Multiple-Recipient MESSAGE Requests in the Session
Initiation Protocol (SIP) (S): [RFC5365] defines a mechanism whereby
a client can send a single SIP MESSAGE to multiple recipients.
This is accomplished by including the list of recipients as an
object in the body, and having a network server send a copy to
each recipient.
3.2. Session ModeRFC 4975, The Message Session Relay Protocol (MSRP) (S): [RFC4975]
defines a small text-based protocol for exchanging arbitrarily
sized content of any kind between users. An MSRP session is set
up by exchanging certain information, such as an MSRP URI, within
SIP and SDP signaling.
RFC 3862, Common Presence and Instant Messaging (CPIM): Message
Format (S): [RFC3862] defines a wrapper around instant message
content, providing meta-data such as the sender and recipient
identity. The CPIM format is carried in MSRP.
RFC 4976, Relay Extensions for the Message Sessions Relay Protocol
(MSRP) (S): [RFC4976] adds support for relays to MSRP. These relay
servers receive MSRP messages and send them towards the
destination. They provide support for firewall and NAT traversal,
and allow for features such as recording and inspection to be
implemented.
RFC 6135, An Alternative Connection Model for the Message Session
Relay Protocol (MSRP) (S): [RFC6135] Allows clients to negotiate
which endpoint in a session will establish the MSRP connection.
Without this specification, the client generating the SDP offer
would initiate the connection.
RFC 6714, Connection Establishment for Media Anchoring (CEMA) for the
Message Session Relay Protocol (MSRP) (S): [RFC6714] allows
middleboxes to anchor the MSRP connection, without the need for
middleboxes to modify the MSRP messages, and thus also enables a
secure end-to-end MSRP communication in networks where such
middleboxes are deployed.
3.3. IM Chat Rooms
In SIMPLE, IM multi-user chat, also known as chat-rooms, are provided
using regular SIP conferencing mechanisms. The framework for SIP
conferencing [RFC4353] and conference control [RFC5239] describe how
all SIP-based conferencing works, including joining and leaving,
persistent and temporary conferences, floor control and moderation,
and learning of conference membership, amongst other functions. All
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Internet-Draft Simple Made Simple February 2013
that is necessary are extensions to provide features that are
specific to IM.
draft-ietf-simple-chat, Multi-party Chat Using the Message Session
Relay Protocol (MSRP) (S): [I-D.ietf-simple-chat] defines how MSRP
is used to provide support for nicknames and private chat within
an IM conference.
3.4. IM Features
Several specifications have been written to provide IM-specific
features for SIMPLE. These include "is-typing" indications, allowing
a user to know when their messaging peer is composing a response, and
delivery notifications, allowing a user to know when their IM has
been received.
RFC 3994, Indication of Message Composition for Instant Messaging
(S): [RFC3994] defines an XML format that can be sent in instant
messages that indicates the status of message composition. This
provides the familiar "is-typing" indication in IM systems, but
also supports voice, video and other message types.
RFC 5438, Instant Message Disposition Notification (S): [RFC5438]
provides delivery notifications of IM receipt. This allows a user
to know with certainty that a message has been received.
4. Security Considerations
This specification is an overview of existing specifications, and
does not introduce any security considerations on its own.
5. IANA Considerations
None.
6. Acknowledgements
Thanks to Vijay Gurbani, Barry Leiba, Stephen Hanna, and Salvatore
Loreto for their review and comments.
7. Informative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
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